LCD devices are used as displays on a variety of devices such as, for example, computer monitors and motor vehicle cruise control panels. Existing LCD types include, for example, the twisted nematic liquid crystal display (TN-LCD) and the in-plane switching liquid crystal display (IPS-LCD). The TN-LCD often has the problem of a narrow viewing angle, and so the IPS-LCD was developed to overcome this disadvantage. The IPS-LCD typically has one or more common electrodes and a plurality of pixel electrodes all disposed on one of two opposite substrates. The electrodes drive liquid crystal molecules interposed between the substrates with an electric field. The resulting electric field is substantially in a plane parallel to the substrates. Such a configuration provides a wide viewing angle.
However, the common electrodes and pixel electrodes are formed of opaque metals, giving the IPS-LCD a low aperture ratio and low transmittance. Thus a fringe field switching liquid crystal display (FFS-LCD) with a flat plate-like common electrode has been developed in order to improve on the aperture ratio and transmittance. The FFS-LCD is characterized by its driving electric field, which is between each pixel electrode and the common electrode. Because the common electrode is transparent, the FFS LCD can typically attain a higher aperture ratio and a higher transmittance.
FIG. 4 is a schematic, cross-sectional view of a conventional FFS-LCD 1. The FFS-LCD 1 includes an upper substrate 20 and an opposite lower substrate 10, with the substrates 20, 10 being spaced apart a predetermined distance. A liquid crystal layer 50 having a multiplicity of liquid crystal molecules (not labeled) is disposed between the upper and lower substrates 20, 10. A backlight module (not shown) is disposed under the lower substrate 10 for providing illumination.
A common electrode 11 and a plurality of pixel electrodes 13 are disposed at the lower substrate 10, with an insulating layer 15 interposed between the common electrode 11 and the pixel electrodes 13. A lower alignment film 14 is formed on the insulating layer 15, such that the lower alignment film 14 also covers the pixel electrodes 13. A color filter 25 and an upper alignment film 24 are formed on an inner surface of the upper substrate 20, in that order from top to bottom.
Also referring to FIG. 5, two gate lines 3 and two data lines 7 define a pixel area of the FFS-LCD 1. The data lines 7 are parallel to but spaced apart from each other, and are substantially perpendicular to the gate lines 3.
Pixel electrodes 13 and common electrode 11 are formed in the pixel area. The pixel and common electrodes 13, 11 are made of a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The pixel electrodes 13 include a plurality of comb portions (not labeled) substantially parallel to each other, and are electrically connected to the source line 7a of the TFT (not labeled) through a contact hole thereof.
The comb portions of the pixel electrodes 13 are parallel to each other, and are all oriented in a first direction. When the FFS-LCD 1 is driven, a fringe electric field is formed between the common electrode 11 and each pixel electrode 13. The liquid crystal molecules disposed over the common electrode 11 and pixel electrodes 13 are driven by this electric field and have a corresponding orientation. Then, the liquid crystal molecules are rotated only in a single direction. This means that an associated display screen exhibits color shift when the display screen is obliquely viewed while displaying white.
Referring to FIG. 6, a schematic, plan view of a pixel area of another FFS-LCD is shown. Comb portions of pixel electrodes 23 are substantially parallel to each other. Each comb portion has an elbow section, such that the comb portion is bent. When a voltage is applied between the pixel and common electrodes 23, 21, a horizontal in-plane electric field in two directions is established between the pixel and common electrodes 23, 21. Then, the liquid crystal display device has two domains so as to reduce color shift.
However, because each of the comb portions of the pixel electrodes 23 includes an elbow portion, and the electric field yielded near the elbow portion is liable to be distorted. Liquid crystal molecules at the elbow portion may be or abnormally oriented. Thus, the display quality of the FFS-LCD would be impaired.
What is needed, therefore, is a fringe field switching mode liquid crystal display device which has reduced color shift and which provides relatively uniform display quality.